I used to use Pyblosxom to run my blog. Its extreme simplicity, ease of setup, and large number of plugins was appealing to me. However, it's a CGI app, which means it's slow, and it doesn't give you any help with cookies, forms, authentication, etc, etc.
Thus, I set out to write a blog server inspired by Pyblosxom, but which used a modern framework. Thus was born Cherry Blossom, the code which currently runs this site. Since I was a developer on Pyblosxom, I can tell you that it has an extremely similar design, modified in places where I thought it could use updating. It should parse Pyblosxom blog entries without any changes.
After I analyzed some Haskell code to generate roman numerals that I saw on reddit and really liked, I explored the same problem in python. To do so, I wrote an iterative unfold for python, which, to my knowledge, had not been done before.
I couldn't easily find a code snippet for iterating backwards over a file in python, so I wrote one, and learned a bit about optimization on the way.
The title's pretty self-explanatory. The code's described further here.
I was pissed off when Guido added decorators to Python. I thought they were unnecessary syntactic sugar which were starting us on the road to Perl-like TMTOWTDI. My stance has softened a bit since (I use the @expose decorator in Cherry Blossom, but I still am very hesitant to use other decorators), but at the time I was furious.
In response, I wrote my most controversial piece of code ever, The redecorator. It simply parses a python file and turns all decorators into the equivalent assignment statement after the end of the method. Utterly useless, but it was a fun state machine to write.
There were a lot of comments on it at the time - I responded to them here.
I wrote a simple utility script to dump out a limited number of rows from a mysql database, which I used to set up the test environment at my current job.
When I saw a goofy programming problem on reddit, I just had to solve it.
I convinced my company to convert to subversion from sourcesafe, and by doing so I volunteered to do the conversion. I found an excellent program that helped me do the conversion, but required a bit more cleanup once it was done. So I wrote a quickie script.
In 2005, Illinois only lost one regular season basketball game. Somebody pointed out that the worst team in basketball had beaten them, transitively, through 7 teams. I wanted to know if every team had "beaten" illinois in the same way that year, so I found out.